In the field of magnetic domain devices, materia-s that exhibit magnetic domain characteristics, the behavior of such magnetic domains, and the use of these magnetic domain materials in sensing and display devices have been described: see United Kingdom Pat. No. 1,180,334; Krumme, J-P et al., "Ferrimagnetic Garnet Films for Magnetooptic Information Storage", IEEE Transactions on Magnetics, Vol. Mag-11, No. 5, Sept. 1975, page 1097; Lacklison, D.E. et al., "The Magnetooptic Bubble Display", IEEE Transactions on Magnetics, Vol. Mag-13, No. 3, May 1977, page 973; Lacklison, E.E. et al., "Magneto-Optic Displays", IEEE Transactions on Magnetics, Vol. Mag-11, No. 5, Sept. 1975, page 1118; Hill, B. And Schmidt, K.P., "Fast Switchable Magneto-Optic Memory Display Components", Phillips Journal of Research, Volume 33, Nos. 5/6, 1978, page 211; Almasi, G.S., "Magnetooptic Bubble-Domain Devices", IEEE Transactions on Magnetics, Vol. Mag-7, No. 3, Sept. 1971, page 370; U.S. Pat. No. 3,815,107; and U.S. Pat. No. 3,526,883.
Certain magnetic domain or magneto-optic display devices change or switch the direction of magnetization M of a magnetic material formed into individual post elements through electrical conductors or drive -ines that establish a magnetic field having an opposite direction of magnetization. ("Fast Switchable Magneto-Optic Memory Display Components", supra; and U.S. Pat. No. 4,114,191). An external bias field may be required (U.S. Pat. No. 4,114,191) or it may be omitted (United Kingdom Pat. No. 1,180,334). When a magnetic field is estab-ished having a strength equal to or greater than Hk-4.pi.Ms, the reversal of the direction of magnetization or switching occurs.
This process of switching involves two parts: nucleation of a domain wall and the movement or propagation of the domain wall toward or to complete saturation. A magnetic domain wall is established by nucleation within the magnetic material of the selected post element. This domain wall is formed between opposite orientations of M at the interface between the initial condition of magnetization and the nucleated opposite magnetic condition. The remainder of the element is switched by propagating the domain wall through the thickness of the element so that part or all of the entire element exhibits a direction of magnetization opposite to the initial condition, i.e., partial or complete saturation.
It is known that the magnetic field required for nucleation is greater than that required for propagating the domain wall because wall motion is limited by demagnetizing and coercivity effects. The field established by the selected row-and-column conductors diminishes rapidly as the distance from the conductors increases. Thus, it is understood that value of the magnetic field adjacent to the energized conductors is large whi-e the field in the region of the post element opposite the energized conductors is relatively small. Therefore, a much larger field is required to propagate the domain wall across the post element where only a single row and a single column conductor are energized.
This invention, an apparatus and method for switching a magnetic domain lens enhances the switching process in a magnetic material, particularly in that material which is formed into pixel or post elements, by directing an additional electrical current in a selected third electrical conductor during or subsequent to the coincident current selection of a row and a column conductor which cross and adjoin a selected post element of the magnetic domain lens. In so doing, the efficiency of the magnetic domain lens is substantially increased by propagating the domain wall across the post element with reduced electrical current in the selected paired and third conductors.